Image display apparatus and head mounted display

ABSTRACT

An image display apparatus includes: an image forming device; an optical system converting light emitted from the image forming device into parallel light; and an optical device to which the light beams converted into the parallel light by the optical system enter, in which the light beams are guided, and from which the light beams are emitted, wherein a central light beam emitted from the center of the image forming device, passing through the nodal point of the optical system and entering the optical device at an optical device center point intersects an XY plane defined by an X axis that passes through the optical device center point, and is parallel to the axis direction of the optical device and a Y axis that passes through the optical device center point, and coincides with the normal axis of the optical device at angles other than 0 degree.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image display apparatus used inorder to allow an observer to observe a two-dimensional image formed byan image forming device, and relates to a head mounted display (HMD)having the image display apparatus incorporated therein and including aframe shaped like glasses to be worn on the head of an observer.

2. Description of the Related Art

A virtual-image display apparatus (image display apparatus) in which avirtual-image optical system allows an observer to view, as an enlargedvirtual image, a two-dimensional image formed by an image forming deviceis widely known from JP-A-2006-162767.

As shown in FIG. 1 which is a conceptual view, an image displayapparatus 100 includes an image forming device 111 having a plurality ofpixels arrayed in a two-dimensional matrix, a collimating optical system112 for collimating light emitted from the pixels of the image formingdevice 111, and an optical device (a light guide means) 120 on which thelight collimated by the collimating optical system 112 is incident. Theincident light is guided and emitted from the optical device. Theoptical device 120 includes a light guide plate 121, a first deflectingmember 130 (e.g., a single-layer light reflective film), and a seconddeflecting member 140 (e.g., a light reflective multilayer film having amultilayer laminated structure). Incident light propagates in the lightguide plate 121 by total reflection and is then emitted from the lightguide plate 121. The first deflecting member 130 reflects the lightincident on the light guide plate 121 so that light incident on thelight guide plate 121 is totally reflected in the light guide plate 121,and the second deflecting member 140 emits the light, which propagatesin the light guide plate 121 by total reflection, from the light guideplate 121. For example, if HMD is formed by such an image displayapparatus 100, the reduction in weight and size of an apparatus can beachieved.

Further, a virtual-image display apparatus (image display apparatus)using a hologram diffraction grating, in which a virtual-image opticalsystem allows an observer to view, as an enlarged virtual image, atwo-dimensional image formed by an image forming device is widely knownfrom JP-A-2007-94175.

As shown in FIG. 6 which is a conceptual view, an image displayapparatus 300 basically includes an image forming device 111 fordisplaying an image, a collimating optical system 112, and an opticaldevice (a light guide means) 320 on which the light displayed by theimage forming device 111 is incident. Incident light is guided to an eye41 of an observer. Here, the optical device 320 includes a light guideplate 321, and first and second diffraction grating members 330 and 340provided on the light guide plate 321. Each of the first and seconddiffraction grating members 330 and 340 is formed by a reflective volumehologram diffraction grating. Light emitted from pixels in the imageforming device 111 enters the collimating optical system 112, where thelight is converted into parallel light, and the parallel light entersthe light guide plate 321. The parallel light is incident on and isemitted from a first surface 322 of the light guide plate 321. On theother hand, the first and second diffraction grating members 330 and 340are attached to a second surface 323 of the light guide plate 321parallel to the first surface 322.

SUMMARY OF THE INVENTION

When an observer views a horizontally located object in a see-throughtype head mounted display, in order to prevent a display image frombecoming an obstacle, it is necessary to shift and display the displayimage to above or below the line of sight of an observer in a horizontaldirection (referred to a “horizontal line of sight of an observer”). Insuch a case, in the related art, the whole image display apparatus 100or 300 is arranged, for example, below the horizontal line of sight ofthe observer (refer to FIG. 13). That is, the image forming device 111is attached to temple portions of a frame shaped like glasses, using anattaching member, in order to be worn on the head of an observer.

Meanwhile, the image display apparatus 100 or 300 in the related art isdesigned so that a central light beam CL that is emitted from the centerof the image forming device 111, and passes through the principal point(hereinafter may be referred to as a “front principal point”) of thecollimating optical system 112 on the side of the image forming deviceimpinges on the light guide plate 121 or 321 perpendicularly. That is,the central light beam CL is designed to enter the light guide plate 121or 321 at a zero incidence angle. In this case, the center of an imageto be displayed coincides with a perpendicular direction of the firstsurface 122 or 322 of the light guide plate 121 or 321.

The basic configuration of the image display apparatus (represented bythe image display apparatus 100) in the related art is shown in FIGS.14A and 14B. The central light beam CL emitted from the center of theimage forming device 111 on the optical axis of the collimating opticalsystem 112 is converted into substantially parallel light by thecollimating optical system 112, and then enters the first surface(incident surface) 122 of the light guide plate 121 perpendicularly.Then, the light travels along a propagation direction A while beingtotally reflected between the first surface 122 and the second surface123 by the first deflecting member 130. Subsequently, the central lightbeam CL is reflected and diffracted by the second deflecting member 140,is emitted perpendicularly from the first surface 122 of the light guideplate 121, and reaches the eye 41 of an observer.

However, in such a related art, as shown in FIG. 13, it is necessary totilt the whole image display apparatus 100 by an angle θ″. Particularlywhen the size of the image display apparatus 100 is large, there is aproblem in that the angle θ″ by which the image display apparatus 100can be tilted is limited or the degree of freedom in design becomes low,from the relationship with an attaching portion (a temple portion) of aframe shaped like glasses for being worn on the head of the observer.

Further, an observable region (pupil diameter) of the image displayapparatus is typically as small as about 6 mm. Thus, when the imagedisplay apparatus is moved in the vertical direction by pivoting theimage display apparatus, there is a risk that an image emitted from theimage display apparatus may be moved away from the eyes of an observerif the axis of this pivoting is greatly shifted from a virtual straightline connecting the centers of two eyeballs of an observer who observesthe image forming device.

Therefore, it is desirable to provide an image display apparatusallowing an arrangement with a high degree of freedom and having a highdegree of freedom in design so as not to become an obstacle to ahorizontal line of sight of an observer, and a head mounted display inwhich the image display apparatus is incorporated. It is also desirableto provide a head mounted display that prevents an image emitted from animage display apparatus from being moved away from the eyes of anobserver, even when the image display apparatus is moved in a verticaldirection by pivoting the image display apparatus.

According to one embodiment of the invention, there is provided an imagedisplay apparatus including:

(A) an image forming device;

(B) an optical system that converts light emitted from the image formingdevice into parallel light; and

(C) an optical device to which the light beams converted into theparallel light by the optical system enter, in which the light beams areguided, and from which the light beams are emitted.

Here, when a point where a central light beam that is emitted from thecenter of the image forming device and passes through the nodal point ofthe optical system on the side of the image forming device enters theoptical device is defined as an optical device center point, an axisthat passes through the optical device center point, and is parallel tothe axis direction of the optical device is defined as an X-axis, and anaxis that passes through the optical device center point, and coincideswith the normal axis of the optical device is defined as a Y-axis,

the central light beam intersects the XY plane at angles other than 0degree.

According to a first embodiment of the invention a head mounted displayis a head mounted display including:

(a) a frame shaped like glasses to be worn on the head of the head of anobserver, and

(b) an image display apparatus attached to the frame. The image displayapparatus is formed by the above image display apparatus. The headmounted display of the embodiment of invention may include one imagedisplay apparatus (one-eye type) or two image display apparatuses(both-eyes type) of the embodiment of the invention.

According to a second embodiment of the invention, there is a provided ahead mounted display including:

(a) a frame shaped like glasses to be worn on the head of an observer;and

(b) an image display apparatus attached to the frame, the image displayapparatus including:

(A) an image forming device;

(B) an optical system that converts light emitted from the image formingdevice into parallel light; and (C) an optical device to which the lightbeams converted into the parallel light by the optical system enter, inwhich the light beams are guided, and from which the light beams areemitted.

Here, the image display apparatus is pivotally attached to the frame,with a virtual straight line connecting the centers of two eyeballs ofthe observer who observes the image display apparatus as a pivot axis.

In the image display apparatus according to the embodiment of theinvention or the image display apparatus that forms the head mounteddisplay according to the first embodiment of the invention, the centrallight beam intersects the XY plane at an angle (θ) other than 0 degree.Therefore, there is little limitation to the attachment angle of theimage display apparatus when the image display apparatus is attached tothe attaching portion of a frame shaped like glasses, and a high degreeof freedom in design can be obtained. Further, the image displayapparatus that forms the head mounted display according to the secondembodiment of the invention is pivotally attached to a frame, with avirtual straight line connecting the centers of two eyeballs of anobserver who observes the image display apparatus as a pivot axis. Thus,the possibility that an image emitted from the image display apparatusmay be moved away from the eyes of an observer is low, even when theimage display apparatus is moved in a vertical direction by pivoting theimage display apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram of an image display apparatus of Example1.

FIGS. 2A and 2B are views schematically showing the propagation of lightin a light guide plate that forms the image display apparatus of Example1, and conceptual diagrams showing an arrangement state of the lightguide plate, etc.

FIG. 3 is a schematic view when a head mounted display of Example 1 isviewed from above.

FIG. 4 is a schematic view when the head mounted display of Example 1 isviewed from the side.

FIG. 5 is a conceptual diagram of an image display apparatus of Example2.

FIGS. 6A and 6B are conceptual diagrams of an image display apparatus ofExample 3.

FIG. 7 is a conceptual diagram of an image display apparatus of Example4.

FIGS. 8A and 8B are views schematically showing the propagation of lightin a light guide plate that forms an image display apparatus of Example5, and conceptual diagrams showing an arrangement state of the lightguide plate, etc.

FIG. 9 is a view when a state where an image display apparatus ofExample 6 is worn on the head of an observer is obliquely viewed.

FIG. 10 is a view when the state where the image display apparatus ofExample 6 is worn on the head of an observer is viewed from the front.

FIG. 11 is a view when the state where the image display apparatus ofExample 6 is worn on the head of an observer is viewed from the side.

FIG. 12 is a view when the state where the image display apparatus ofExample 6 is worn on the head of an observer is viewed from above.

FIG. 13 is the schematic view when a head mounted display in the relatedart is viewed from the side.

FIGS. 14A and 14B are views schematically showing the propagation oflight in a light guide plate that forms the image display apparatus inthe related art, and conceptual diagrams showing an arrangement state ofa light guide plate, etc. that forms an image display apparatus in therelated art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, although the invention will be described on the basis ofembodiments with reference to the drawings, the invention is not limitedto the embodiments, and various numeric values and materials in theembodiments are illustrative. Description will be given in the followingorder.

1. Overall description relating to image display apparatus and headmounted display of the invention

2. Example 1 (image display apparatus according to one embodiment of theinvention, and head mounted display according to first embodiment of theinvention

3. Example 2 (modification of Example 1)

4. Example 3 (another modification of Example 1)

5. Example 4 (another modification of Example 1)

6. Example 5 (another modification of Example 1)

7. Example 6 (head mounted display according to second embodiment of theinvention), and others

Overall Description Relating to Image Display Apparatus and Head MountedDisplay of the Invention

A head mounted display according to the first embodiment of theinvention can be configured so that an image display apparatus ispivotally attached to a frame, with a virtual straight line connectingthe centers of two eyeballs of an observer who observes the imagedisplay apparatus as a pivot axis. The head mounted display according tothe first embodiment of the invention having this configuration, or ahead mounted display according to the second embodiment of the inventioncan be configured so that at least one of the image forming device, theoptical system, and the optical device is pivotally attached to theframe. Further, in the head mounted display according to the secondembodiment of the invention including such a configuration, when anobserver views a horizontally located object (for example, a horizontaldirection, an object at an infinite distance, a horizon, or a horizontalline), a depression angle can be formed by the central light beam thatis emitted from the optical device and enter the eyes of the observer.For example, 5 degrees to 45 degrees can be exemplified as thedepression angle with respect to the horizontal plane.

In the image display apparatus according to the embodiment of theinvention, and an image display apparatus that forms the head mounteddisplay according to the first embodiment of the invention including theabove preferable configuration (hereinafter, these are generically andsimply referred to as the “image display apparatuses according to theembodiment of the invention”), it is preferable from the viewpoint ofease of handling, setting, and attachment of the image display apparatusthat the central light beam be included in the YZ plane.

In the image display apparatuses according to the first embodiment ofthe invention including the above preferable embodiment, the opticalaxis of the optical system is included in the YZ plane and intersectsthe XY plane at angles other than 0 degree. Alternatively, the imagedisplay apparatuses can be configured so that the optical axis of theoptical system is parallel to the YZ plane, is parallel to the XY plane,and passes through a position shifted from the center of the imageforming device.

Further, in the head mounted display according to the first embodimentof the invention including the above preferable embodiment andconfiguration, the head mounted display can be configured so that,assuming that the XY plane coincides with the horizontal plane, theangle θ at which the central light beam CL intersects the XY plane is anelevation angle. That is, the central light beam impinges on the XYplane toward the XY plane from below the XY plane. In this case, it ispreferable that the XY plane intersects the vertical plane at anglesother than 0 degree, and it is also preferable that the XY planeintersects the vertical plane at an angle θ. In addition, although themaximum value of 0 is not limited, the maximum value can be 5 degrees.Here, the horizontal plane is a plane including a line of sight (“ahorizontal line of sight of an observer”) when the observer views ahorizontally located object (for example, a horizontal direction, anobject at an infinite distance, a horizon, or a horizontal line), andincluding two eyes of the observer which are horizontally located. Thevertical plane is a plane that is perpendicular to the horizontal planeand includes two eyes of a horizontally located observer.

Alternatively, in the head mounted display according to the first orsecond embodiment of the invention, when an observer views ahorizontally located object (for example, a horizontal direction, anobject at an infinite distance, a horizon, or a horizontal line), adepression angle can be formed by the central light beam that is emittedfrom the optical device and enters the eyes of the observer. Forexample, 5 degrees to 45 degrees can be exemplified as the depressionangle with respect to the horizontal plane.

In the image display apparatus according to the first embodiment of theinvention including the preferable embodiment and configurationdescribed above, and an image display apparatus that forms the headmounted display according to the second embodiment of the invention(hereinafter, these are generically and simply referred to as the “imagedisplay apparatuses according to the embodiment of the invention”), theoptical device includes:

(a) a light guide plate from which incident light is emitted after thelight propagates in the light guide plate by total reflection;

(b) a first deflecting member that deflects the light incident on thelight guide plate so that the light incident on the light guide plate istotally reflected in the light guide plate; and

(c) a second deflecting member that deflects the light, which propagatesin the light guide plate by total reflection, multiple times so as toemit the light, which propagates in the light guide plate by totalreflection, from the light guide plate.

Here, the central point of the first deflecting member is an opticaldevice center point. The term “total reflection” refers to totalinternal reflection or total reflection in the light guide plate. Thisalso applies to the following.

Here, the first deflecting member can reflect the light incident on thelight guide plate, and the second deflecting member can transmit andreflect the light, which propagates in the light guide plate by totalreflection, multiple times. In this case, the first deflecting membercan function as a reflecting mirror, and the second deflecting membercan function as a semi-transmissive mirror.

In this configuration, the first deflecting member can be formed by, forexample, a light reflective film (a kind of mirror) made of metalincluding an alloy and configured to reflect the light incident on thelight guide plate, or a diffraction grating (e.g., a hologramdiffraction grating film) for diffracting the light incident on thelight guide plate. The second deflecting member can be formed by amultilayer laminated structure in which multiple dielectric laminatedfilms are laminated, a half mirror, a polarizing beam splitter, or ahologram diffraction grating film. Although the first deflecting memberand the second deflecting member are disposed (incorporated) in thelight guide plate, the first deflecting member reflects or diffractsparallel light incident on the light guide plate so that the incidentparallel light is totally reflected in the light guide plate. On theother hand, the second deflecting member reflects or diffracts theparallel light, which propagates in the light guide plate by totalreflection, multiple times, and emits the parallel light from the lightguide plate.

Alternatively, the first deflecting member can diffract the lightincident on the light guide plate, and the second deflecting member candiffract the light, which propagates in the light guide plate by totalreflection, multiple times. In this case, the first deflecting memberand the second deflecting member each can be formed by a diffractiongrating element. Further, the diffraction grating element can be formedby a reflective diffraction grating element or a transmissivediffraction grating element. Alternatively, one of the diffractiongrating elements can be formed by a reflective diffraction gratingelement, and the other diffraction grating element can be formed by atransmissive diffraction grating element. An example of the reflectivediffraction grating element can include a reflective volume hologramdiffraction grating. For convenience, the first deflecting member formedby a reflective volume hologram diffraction grating is sometimesreferred to as a “first diffraction grating member”, and the seconddeflecting member formed by a reflective volume hologram diffractiongrating is sometimes referred to as a “second diffraction gratingmember”.

When an image display in color is performed by the image displayapparatuses according to the embodiment of the invention, in order todiffract or reflect a P-number of (e.g., three corresponding to red,green, and blue) types of light beams having a P-number of differentwavelength bands (or wavelengths), in the first diffraction gratingmember or the second diffraction grating member, a P-number ofdiffraction grating layers, each formed by a reflective volume hologramdiffraction grating, can be laminated. Each diffraction grating layer isformed with interference fringes corresponding to one wavelength band(or wavelength). Alternatively, in order to diffract or reflect aP-number of types of light beams having a P-number of differentwavelength bands (or wavelengths), the first diffraction grating memberor the second diffraction grating member can be formed by onediffraction grating layer that is provided with a P-number of types ofinterference fringes. Alternatively, for example, the angle of view canbe divided into three parts, and the first diffraction grating member orthe second diffraction grating member can be formed by laminatingdiffraction grating layers corresponding to the parts of the angle ofview. By adopting these structures, it is possible to increase thediffraction efficiency and acceptable diffraction angle and to optimizethe diffraction angle when the light beams having the wavelength bands(or wavelengths) are diffracted or reflected by the first diffractiongrating member or the second diffraction grating member.

An example of the material that forms the first diffraction gratingmember and the second diffraction grating member can include aphotopolymer material. The material and basic structure of the firstdiffraction grating member and the second diffraction grating memberformed by the reflective volume hologram diffraction gratings may be thesame as those of the reflective volume hologram diffraction gratings inthe related art. The reflective volume hologram diffraction gratingrefers to a hologram diffraction grating that diffracts and reflectsonly +1-order diffracted light. Although the diffraction grating memberis formed with interference fringes extending from the inner side to theouter side of the diffraction grating member, a formation method for theinterference fringes may be the same as that adopted in the related art.Specifically, for example, the material that forms the diffractiongrating member (e.g., a photopolymer material) is irradiated with objectlight in a first predetermined direction, and is simultaneouslyirradiated with reference light in a second predetermined direction,whereby the object light and the reference light may form interferencefringes in the material that forms the diffraction grating member. Byappropriately selecting the first predetermined direction, the secondpredetermined direction, and the wavelengths of the object light and thereference light, the interference fringes can be arranged at a desiredpitch with a desired slant angle on the surfaces of the diffractiongrating member. Here, the slant angle of the interference fringes refersto the angle formed between the surfaces of the diffraction gratingmember (or the diffraction grating layer) and the interference fringes.When the first diffraction grating member and the second diffractiongrating member are formed to have a laminated structure in which aP-number of diffraction grating layers, each formed by a reflectivevolume hologram diffraction grating, are laminated, a P-number ofdiffraction grating layers are separately formed, and are then laminated(bonded) with, for example, an ultraviolet curing resin adhesive.Alternatively, a P-number of diffraction grating layers may be formed byforming one diffraction grating layer of an adhesive photopolymermaterial, and then bonding layers of an adhesive photopolymer materialthereon in order.

Alternatively, the image display apparatuses according to the embodimentof the invention can be embodied so that the optical device is formed bya semi-transmissive mirror that the light emitted from the image formingdevice enters and from which the light is emitted toward the eyes of anobserver. The light emitted from the image forming device can enter thesemi-transmissive mirror after propagating in the air, or afterpropagating in a transparent member such as a glass plate or a plasticplate (specifically, a member formed of a material similar to a materialthat forms the light guide plate, that will be described below). Thesemi-transmissive mirror may be attached to the image forming device viathe transparent member or via a member different from the transparentmember.

The image display apparatuses according to the embodiment of theinvention including the preferable embodiments and configurationsdescribed above can be embodied so that the image forming device has aplurality of pixels arrayed in a two-dimensional matrix. Forconvenience, the image forming apparatus having this configuration isreferred to as an image forming device having a first configuration.

In the image forming device having the first structure, for example, theimage forming device can be formed by an image forming device includinga reflective spatial light modulator and a light source, an imageforming device including a transmissive spatial light modulator and alight source, or an image forming device including a light emittingelement such as an organic EL (Electro Luminescent) element, aninorganic EL element, or a light emitting diode (LED). Especially, it ispreferable that the image forming device includes a reflective spatiallight modulator and a light source. For example, the spatial lightmodulator can be formed by a light valve, a transmissive or reflectiveliquid crystal display such as an LCOS (Liquid Crystal On Silicon), or adigital micromirror device (DMD), and the light source can be formed bya light emitting element. Further, the reflective spatial lightmodulator can include a liquid crystal display and a polarizing beamsplitter that reflects and guides part of the light from the lightsource to the liquid crystal display and transmits and guides part ofthe light reflected by the liquid crystal display to an optical system.The light emitting element that forms the light source can include, forexample, a red light emitting element, a green light emitting element, ablue light emitting element, and a white light emitting element, orwhite light may be obtained by performing color mixture and luminanceequalization for the red light, green light, and blue light emitted fromthe red light emitting element, the green light emitting element, andthe blue light emitting element using light valves. The light emittingelement can be formed by a semiconductor laser element, a solid-statelaser, or an LED. The number of pixels may be determined according tothe specifications of the image display apparatus. For example, aconcrete number of pixels can be 320×240, 432×240, 640×480, 1024×768, or1920×1080.

Alternatively, in the image display apparatuses according to theembodiment of the invention including the preferable embodiments andconfigurations described above, the image forming device can include alight source, and a scanning member that scans the parallel lightemitted from the light source. For convenience, the image formingapparatus having this structure is referred to as “an image formingdevice having a second configuration”.

The light source in the image forming device having the second structurecan include a light emitting element as a light source, morespecifically, a red light emitting element, a green light emittingelement, a blue light emitting element, and a white light emittingelement, or white light may be obtained by performing color mixture andluminance equalization for the red light, green light, and blue lightemitted from the red light emitting element, the green light emittingelement, and the blue light emitting element using light valves. Thelight emitting element can be formed by a semiconductor laser element, asolid-state laser, or an LED. The number of pixels (virtual pixels) inthe image forming device having the second structure can also bedetermined according to the specifications of the image displayapparatus. For example, a concrete number of pixels (virtual pixels) is320×240, 432×240, 640×480, 1024×768, or 1920×1080. When an image displayin color is performed, and the light source includes a red lightemitting element, a green light emitting element, and a blue lightemitting element, for example, it is preferable to perform colorsynthesis using a crossed prism. The scanning member can be formed by aMEMS (Micro Electro Mechanical system) having a micromirror rotatable inthe two-dimensional direction, or a galvanometer mirror, which scanslight emitted from the light source horizontally and vertically.

In the image forming device having a first configuration or the imageforming device having a second configuration, the light converted into aplurality of parallel light beams by an optical system (an opticalsystem which converts emitted light into parallel light beams: may bereferred to as a “parallel light emitting optical system”, andspecifically, for example, a collimating optical system or a relayoptical system) is caused to enter the light guide plate. The reason whythe light beams are to be parallel light beams is based on the fact thatit is necessary to store the light wave surface information when suchlight beams have entered the light guide plate even after the lightbeams have been emitted from the light guide plate via the firstdeflecting member and the second deflecting member. In order to generatea plurality of parallel light beams, for example, an optical emittingportion of the image forming device may be located at a place (position)corresponding to the focal length of the parallel light emitting opticalsystem. The parallel light emitting optical system functions to convertpositional information of pixels into angular information in the opticalsystem of the optical device. For example, the parallel light emittingoptical system can be formed by an optical system which has a positiveoptical power as a whole and which includes a convex lens, a concavelens, an adjustable surface prism, or a hologram lens alone or acombination of these. A light-shielding member having an opening isarranged between the parallel light emitting optical system and thelight guide plate so that the light that is not desired is preventedfrom being emitted from the parallel light emitting optical system andentering the light guide plate.

The light guide plate has two parallel surfaces (first and secondsurfaces) extending parallel to the axis (X-axis) of the light guideplate. Assuming that a surface of the light guide plate on which lightis incident is an incident surface and a surface of the light guideplate from which light is emitted is an exit surface, both the incidentsurface and the exit surface may be defined by the first surface, or theincident surface may be defined by the first surface and the exitsurface may be defined by the second surface. For example, the lightguide plate can be formed of a glass material including optical glasssuch as quartz glass or BK7, or a plastic material (e.g., PMMA,polycarbonate resin, acrylic resin, amorphous polypropylene resin, orstyrene resin including AS resin). The light guide plate is not limitedto a flat plate, and may be curved.

By the image display apparatus according to the embodiment of theinvention, for example, a head mounted display can be constructed, thereduction in weight and size of an apparatus can be achieved, thediscomfort when the apparatus is mounted can be significantlyalleviated, and the manufacture cost can be cut down.

In the head mounted display according to the first and secondembodiments of the invention including the preferable embodiments andconfigurations described above, the frame can include a front portion tobe arranged at the front of an observer; and two temple portionspivotally attached to opposite ends of the front portion via hinges. Anend cover portion is attached to a tip portion of each temple portion.Although the image display apparatus is attached to the frame,specifically, the image forming device may be attached to, for example,the temple portion.

In the head mounted display according to the first or second embodimentof the invention including various kinds of configurations andembodiments described above a nose pad can be attached. That is, when anobserver views the whole head mounted display of the embodiment of theinvention, the assembly of the frame and the nose pad has almost thesame structure as normal eyeglasses except that there is no rim. Thematerial that forms the frame can be the same material as the materialswhich form normal eyeglasses, such as metal, an alloy, or plastic, andcombinations thereof. The nose pad can also have well-knownconfiguration and structure.

In the head mounted display according to the first or second embodimentof the invention, it is desirable from the viewpoints of design or easeof mounting that a wiring line (a signal line, a power line, etc.) thatextends from one or two image forming devices extends to the outsidefrom a tip portion of an end cover portion via a temple portion and theinside of the end cover portion, and is connected to an external circuit(a control circuit). Further, it can be embodied so that each imageforming device includes a headphone portion, and a wiring line for theheadphone portion from each image forming device extends to theheadphone portion via the temple portion and the inside of the end coverportion from the tip portion of the end cover portion. The headphoneportion can include, for example, an inner ear type headphone portionand a canal type headphone portion. More specifically, it is preferablethat the wiring line for the headphone portion extends to the headphoneportion from the tip portion of the end cover portion so as to wraparound behind the auricle (external ear).

The head mounted display according to the first or second embodiment ofthe invention can be used for, for example, the display of a title of afilm; the display of various description in a play, a kabuki, a Noh, akyogen, an opera, a concert, a ballet, various theaters, an amusementpark, an art museum, a tourist resort, a pleasure resort, a sightseeingguide, etc.; the display of various descriptions or symbols, signs,marks, emblems, designs, etc. in the operation, manipulation,maintenance, disassembling, etc. of various apparatuses; the display ofvarious descriptions or symbols, signs, marks, emblems, designs, etc.concerning persons, objects. etc.; and the display of closed captions.

Example 1

Example 1 relates to an image display apparatus according to theembodiment of the invention, and a head mounted display according to afirst embodiment of the invention. A conceptual diagram of the imagedisplay apparatus of Example 1 is shown in FIG. 1, the propagation oflight in alight guide plate that forms the image display apparatus ofExample 1 is schematically shown in FIG. 2A, and a conceptual diagramshowing an arrangement state of the light guide plate, etc. that formsthe image display apparatus of Example 1 is shown in FIG. 2B. Further, aschematic view when the head mounted display of Example 1 is viewed fromabove is shown in FIG. 3, and a schematic view when the head mounteddisplay is viewed from the side is shown in FIG. 4.

In Example 1 or Examples 2 to 6 that will be described below, an imagedisplay apparatus 100, 200, 300, or 400 includes:

(A) an image forming device 111 or 211;

(B) an optical system (parallel light emitting optical system) 112 or254 that converts light emitted from the image forming device 111 or 211into parallel light; and

(C) an optical device 120 or 320 which the light beams converted intothe parallel light by the optical system 112 or 254 enter, and areguided therein, and emitted therefrom.

Further, a head mounted display of Example 1 or Examples 2 to 6 thatwill be described below includes

(a) a frame 10 shaped like glasses to be worn on the head of anobserver, and

(b) the image display apparatus 100, 200, 300, and 400 attached to theframe 10. In addition, although a both-eyes type display including twoimage display apparatuses has specifically been adopted as the headmounted display of the embodiment, a one-eye type display including oneimage display apparatus may be adopted. The image forming device 111 or211 displays a monochromatic image.

In Example 1 or Examples 2 to 6 that will be described below, when thepoint where a central light beam CL that is emitted from the center ofthe image forming device 111 or 211 and passes through the nodal pointof the optical system 112 or 254 on the side of the image forming deviceenters the optical device 120 or 320 is defined as an optical devicecenter point O, an axis that passes through the optical device centerpoint O, and is parallel to the axis direction of the optical device 120or 320 is defined as an X-axis, and an axis that passes through theoptical device center point O, and coincides with the normal axis of theoptical device 120 or 320 is defined as a Y-axis, the central light beamCL intersects the XY plane at angles (θ) other than 0 degree. Thecentral light beam CL is included in the YZ plane.

In Example 1, or Examples 2 to 4, and 6 that will be described below,the optical axis of the optical system 112 or 254 is included in the YZplane, and intersects the XY plane at angles other than 0 degree,specifically, an angle θ (refer to FIGS. 2A and 2B).

In the head mounted display of Example 1, or Examples 2 to 6 that willbe described below, assuming that the XY plane coincides with thehorizontal plane, the angle θ at which the central light beam CLintersects the XY plane is an elevation angle. That is, the centrallight beam CL impinges on the XY plane toward the XY plane from belowthe XY plane. The XY plane intersects a vertical plane at angles otherthan 0 degree, specifically, an angle θ.

In Example 1, θ=5 degrees. More specifically, in such a configuration,the central light beam CL (shown by a dotted line in FIG. 4) is includedin the horizontal plane. The optical device 120 or 320 is tilted by theangle θ with respect to the vertical plane. In other words, the opticaldevice 120 or 320 is tilted by the degree of an angle (90-θ) withrespect to the horizontal plane. Further, a central light beam CL′(shown by a one-dot chain line in FIG. 4) emitted from the opticaldevice 120 or 320 is tilted by an angle 2θ with respect to thehorizontal plane. That is, when an observer views the horizontaldirection and an object at an infinite distance, the central light beamCL′ that is emitted from the optical device 120 or 320 and enters theeyes of the observer forms a depression angle θ′ (=2θ). The angle thatthe central light beam CL′ forms with the normal axis of the opticaldevice 120 or 320 is θ. In FIG. 2A, or FIG. 8A that will be describedbelow, a point where the central light beam CL′ is emitted from theoptical device 120 or 320 is represented by O′, and axes passing throughthe point O′ and parallel to the X-axis, the Y-axis, and the Z-axis arerepresented by an X′-axis, an Y′-axis, and an Z′-axis. In addition, thecentral light beam CL emitted from the center of the image formingdevice 111 or 211 is not limited to the form in which the central lightbeam is included in the horizontal plane, and can be embodied so thatthe central light beam intersects the horizontal plane at a desiredangle degree (may be an elevation angle or a depression angle) otherthan 0 degree. Further, when an observer views the horizontal directionand an object at an infinite distance, it can be embodied so that thecentral light beam CL′ that is emitted from the optical device 120 or320 and enters the eyes of the observer forms an elevation angle.

In Example 1 or Examples 2 to 6 that will be described below, theoptical device 120 or 320 includes:

(a) a light guide plate 121 or 321 from which incident light is emittedafter the light propagates in the light guide plate by total reflection;

(b) a first deflecting member 130 or 330 that deflects the lightincident on the light guide plate 121 or 321 so that the light incidenton the light guide plate 121 or 321 is totally reflected in the lightguide plate 121 or 321; and

(c) a second deflecting member 140 or 340 that deflects the light, whichpropagates in the light guide plate 121 or 321 by total reflection,multiple times so as to emit the light, which propagates in the lightguide plate 121 or 321 by total reflection, from the light guide plate121 or 321. The central point of the first deflecting member 130 or 330is an optical device central point O. The optical device 120 to 320 is asee-through type (semi-transmissive).

Here, in Example 1, the first deflecting member 130 and the seconddeflecting member 140 are disposed in the light guide plate 121. Thefirst deflecting member 130 reflects light incident on the light guideplate 121, and the second deflecting member 140 transmits and reflectsthe light, which propagates in the light guide plate 121 by totalreflection, multiple times. That is, the first deflecting member 130functions as a reflecting mirror, and the second deflecting member 140functions as a semi-transmissive mirror. More specifically, the firstdeflecting member 130 provided in the light guide plate 121 is formed bya light reflective film (a kind of mirror) made of aluminum andconfigured to reflect light incident on the light guide plate 121. Onthe other hand, the second deflecting member 140 provided in the lightguide plate 121 is formed by a multilayer laminated structure in whichmultiple dielectric laminated films are laminated. The dielectriclaminated films include, for example, a TiO2 film made of a highdielectric constant material and a SiO2 film made of a low dielectricconstant material. The multilayer laminated structure in which multipledielectric laminated films are laminated is disclosed inJP-T-2005-521099. Although six dielectric laminated films are shown inthe drawing, the number of dielectric laminated films is not limitedthereto. Thin pieces made of the same material as that of the lightguide plate 121 are sandwiched between the dielectric laminated films.The first deflecting member 130 reflects (or diffracts) parallel lightincident on the light guide plate 121 so that the parallel lightincident on the light guide plate 121 is totally reflected in the lightguide plate 121. On the other hand, the second deflecting member 140reflects (or diffracts) the parallel light, which propagates in thelight guide plate 121 by total reflection, multiple times, and emits theparallel light toward the eye 41 of an observer from the light guideplate 121.

An inclined surface where the first deflecting member 130 is to beformed is formed in the light guide plate 121 by cutting out a portion124 of the light guide plate 121 in which the first deflecting member130 is to be provided, a light reflective film is formed on the inclinedsurface by vacuum deposition, and the cut portion 124 of the light guideplate 121 is then bonded to the first deflecting member 130. Further, amultilayer laminated structure, in which multiple layers made of thesame material (e.g., glass) as that of the light guide plate 121 andmultiple dielectric films (for example, formed by vacuum deposition) arelaminated, is formed, an inclined surface is formed by cutting out aportion 125 of the light guide plate 121 where the second deflectingmember 140 is to be formed, the multilayer laminated structure is bondedto the inclined surface, and the outer side of the light guide plate isshaped by, for example, polishing. Thus, the optical device 120 in whichthe first deflecting member 130 and the second deflecting member 140 areprovided in the light guide plate 121 can be obtained.

Here, in Example 1, or Examples 2 to 6 that will be described below, thelight guide plate 121 or 321 formed of optical glass or a plasticmaterial has two parallel surfaces (first surface 122 or 322 and secondsurface 123 or 323) extending parallel to a light propagation direction(X-axis) by the total internal reflection of the light guide plate 121or 321. The first surface 122 or 322 and the second surface 123 or 323face each other. Parallel light enters from the first surface 122 or 322serving as a light incident surface, propagates in the light guide plate121 by total reflection, and is then emitted from the first surface 122or 322 serving as a light exit surface. However, the invention is notlimited thereto, and the light incidence surface may be formed by thesecond surface 123 or 323, and the light exit surface may be formed bythe first surface 122 or 322.

In Example 1 or Examples 3 that will be described below, the imageforming device 111 is the image forming device having a firstconfiguration, and has a plurality of pixels arrayed in atwo-dimensional matrix. The image forming device 111 includes areflective spatial light modulator 150 and a light source 153 formed bya light emitting diode for emitting white light. The whole image formingdevice 111 is stored in a housing 113 (shown by a one-dot chain line inFIG. 1), an opening (not shown) is provided in the housing 113, andlight is emitted through the opening from the optical system (theparallel light emitting optical system or the collimating opticalsystem) 112. The reflective spatial light modulator 150 includes aliquid crystal display (LCD) 151 formed by an LCOS serving as a lightvalve, and a polarizing beam splitter 152 that reflects and guides partof the light from the light source 153 to the liquid crystal display 151and transmits and guides part of the light reflected by the liquidcrystal display 151 to the optical system 112. The liquid crystaldisplay 151 includes a plurality of (e.g., 640×480) pixels (liquidcrystal cells) arrayed in a two-dimensional matrix. The polarizing beamsplitter 152 has the same configuration and structure as those of therelated art. Unpolarized light emitted from the light source 153impinges on the polarizing beam splitter 152. P-polarized lightcomponents pass through the polarizing beam splitter 152, and areemitted to the outside of the system. On the other hand, S-polarizedlight components are reflected by the polarizing beam splitter 152,enter the liquid crystal display 151, are reflected in the liquidcrystal display 151, and are then emitted from the liquid crystaldisplay 151. Here, light emitted from pixels for displaying white, oflight emitted from the liquid crystal display 151, contains manyP-polarized light components, and light emitted from pixels fordisplaying black contains many S-polarized light components. Therefore,P-polarized light components, of the light that is emitted from theliquid crystal display 151 and impinges on the polarizing beam splitter152, pass through the polarizing beam splitter 152, and are guided tothe optical system 112. On the other hand, S-polarized light componentsare reflected by the polarizing beam splitter 152, and return to thelight source 153. The optical system 112 is formed by, for example, aconvex lens. In order to generate parallel light, the image formingdevice 111 (concretely, the liquid crystal display 151) is arranged at aplace (position) corresponding to the focal length of the optical system112.

The frame 10 is formed by a front portion 11 arranged at the front of anobserver, two temple portions 13 pivotally attached to both ends of thefront portion 11 via hinges 12, and an end cover portion (referred to asa tip cell, an earmuff, and an ear pad) 14 attached to a tip portion ofeach temple portion 13. Further, a nose pad (not shown) is attached tothe frame. Further, each housing 113 is detachably attached to thetemple portion 13 by the attaching member 18. The frame 10 is made ofmetal or plastic. The housing 113 may be attached so that the housingcan be attached to or detached from the temple portion 13 by theattaching member 18. Each housing 113 may be detachably attached to thetemple portion of the frame of the eyeglasses that is possessed by anobserver who possesses and wears the eyeglasses by the attaching member18.

A wiring line (a signal line, a power line, etc.) 15 that extends fromone image forming device 111A extends to the outside from the tipportion of the end cover portion 14 via the temple portion 13 and theinside of the end cover portion 14. Each image forming device 111A or111B includes a headphone portion 16, and a wiring line 17 for theheadphone portion that extends from each image forming device 111A or111B extends to the headphone portion 16 via the temple portion 13 andthe inside of the end cover portion 14 from the tip portion of the endcover portion 14. More specifically, the wiring line 17 for theheadphone portion extends to the headphone portion 16 from the tipportion of the end cover portion 14 so as to wrap around behind theauricle (external ear). By adopting such a configuration, a neat headmounted display can be formed without giving the impression that theheadphone portion 16 and the wiring line 17 for the headphone portion israndomly arranged.

In the image display apparatus of Example 1, or the image displayapparatus that forms the head mounted display of Example 1, the centrallight beam CL intersects the XY plane at an angle (θ) other than 0degree. Here, when the central light beam CL′ that is emitted from theoptical device and enters the eyes of an observer forms the depressionangle θ′, the relationship of θ′=2θ is satisfied. On the other hand, inthe related art, it is necessary to tilt the whole image displayapparatus by the angle θ″ when it is intended to obtain the samedepression angle. Here, the relationship between θ″ and θ is θ″=2θ.Eventually, in the related art, the optical device should be tilted by2θ with respect to the vertical plane. On the other hand, in Example 1,the optical device has only to be tilted by θ with respect to thevertical plane, and the image forming device has only to be horizontallyheld. Therefore, there is little limitation to the attachment angle ofthe image display apparatus when the image display apparatus is attachedto the attaching portion of a frame shaped like glasses, and a highdegree of freedom in design can be obtained. Further, since the tilt ofthe optical device with respect to the vertical plane is smaller thanthat in the related art, a phenomenon that outdoor daylight is reflectedby the optical device and enters the eyes of an observer hardly occurscompared to the related art. Therefore, a high-quality image can bedisplayed.

Example 2

Example 2 is a modification of Example 1. FIG. 5 is a conceptual view ofan image display apparatus 200 in a head mounted display according toExample 2. As shown in FIG. 5, an image forming device 211 in Example 2is formed by an image forming device having a second configuration. Thatis, the image forming device includes a light source 251, and a scanningmember 253 that scans the parallel light emitted from the light source251. More specifically, the image forming device 211 includes:

(a) a light source 251;

(b) a collimating optical system 252 that converts light emitted fromthe light source 251 into parallel light;

(c) a scanning member 253 that scans the parallel light emitted from thecollimating optical system 252; and

(d) a relay optical system 254 that relays and emits the parallel lightscanned by the scanning member 253. In addition, the whole image formingdevice 211 is stored in a housing 213 (shown by a one-dot chain line inFIG. 5), an opening (not shown) is provided in the housing 213, andlight is emitted through the opening from the relay optical system 254.Each housing 213 is detachably attached to the temple portion 13 by theattaching member 18.

The light source 251 includes a light emitting element for emittingwhite light. The light emitted from the light source 251 enters thecollimating optical system 252 having a positive optical power as awhole, and is emitted as parallel light. The parallel light is reflectedby a total reflection mirror 256, is horizontally and vertically scannedby the scanning member 253 formed by an MEMS that can rotate amicromirror in a two-dimensional direction so as to two-dimensionallyscan the incident parallel light, and is converted into a kind oftwo-dimensional image, whereby virtual pixels (the number of pixels canbe made the same as that of Example 1) are generated. The light from thevirtual pixels passes through the relay optical system 254 formed by arelay optical system of the related art, and light beams converted intoparallel light enter the optical device 120.

The light beams converted into the parallel light by the relay opticalsystem 254 enter the optical device 120, and are guided therein, andemitted therefrom. Since the optical device 120 has the sameconfiguration and structure as that of the optical device adopted inExample 1, a detailed description thereof is omitted. Further, since thehead mounted display of Example 2 has substantially the sameconfiguration and structure as those of the head mounted display ofExample 1 except that the image forming device 211 is different, asdescribed above, a detailed description thereof is omitted.

Example 3

Example 3 is also a modification of Example 1. FIG. 6A is a conceptualview of an image display apparatus 300 in a head mounted displayaccording to Example 3. FIG. 6B is an enlarged schematic sectional viewof a part of a reflective volume hologram diffraction grating. InExample 3, an image forming device 111 is formed by an image formingdevice having a first configuration, similarly to Example 1. An opticaldevice 320 has the same basic configuration and structure as those ofthe optical device 120 of Example 1 except in the configuration andstructure of a first deflecting member and a second deflecting member.

In Example 3, the first deflecting member and the second deflectingmember are disposed on a surface of the light guide plate 321(concretely, a second surface 323 of the light guide plate 321). Thefirst deflecting member diffracts light incident on the light guideplate 321, and the second deflecting member diffracts the light, whichpropagates in the light guide plate 321 by total reflection, multipletimes. Here, each of the first and second deflecting members is formedby a diffraction grating element, specifically, a reflective diffractiongrating element, and more specifically, a reflective volume hologramdiffraction grating. In the following description, for convenience, thefirst deflecting member formed by a reflective volume hologramdiffraction grating is sometimes referred to as a “first diffractiongrating member 330”, and the second deflecting member formed by areflective volume hologram diffraction grating is sometimes referred toas a “second diffraction grating member 340”.

In Example 3, or Example 4 that will be described below, in each of thefirst diffraction grating member 330 and the second diffraction gratingmember 340, one diffraction grating layer is laminated. Each diffractiongrating layer made of a photopolymer material is formed withinterference fringes corresponding to one wavelength band (orwavelength), and the interference fringes are formed by a method in therelated art. The interference fringes formed on the diffraction gratinglayers (diffraction optical elements) linearly extend at a fixed pitchand parallel to the Z-axis direction. The axis of the first diffractiongrating member 330 and the axis of the second diffraction grating member340 are parallel to the X-axis, and the normal axis is parallel to theY-axis.

FIG. 6B is an enlarged schematic partial sectional view of a reflectivevolume hologram diffraction grating. The reflective volume hologramdiffraction grating is formed with interference fringes having a slantangle φ. Here, the slant angle φ refers to the angle formed between thesurface of the reflective volume hologram diffraction grating and theinterference fringes. The interference fringes are formed to extend fromthe inner side to the outer side of the reflective volume hologramdiffraction grating. The interference fringes satisfy the Braggcondition. Here, the Bragg condition is to satisfy the followingExpression A. In Expression A, m is a positive integer, λ represents thewavelength, d represents the pitch of the grating surface (distancebetween virtual planes including interference fringes in the normaldirection), and Θ represents the supplementary angle of the incidenceangle on the interference fringes. When light enters the diffractiongrating member at an incidence angle ψ, the supplementary angle Θ, theslant angle ψ, and the incidence angle ψ have the relationship given byExpression B:M·λ=2·d·sin(Θ)  (A)Θ=90°−(φ+ψ)  (B)

As described above, the first diffraction grating member 330 is disposed(bonded) on the second surface 323 of the light guide plate 321, anddiffracts and reflects parallel light incident on the light guide plate321 from the first surface 322 so that the parallel light incident onthe light guide plate 321 is totally reflected in the light guide plate321. Further, as described above, the second diffraction grating member340 is disposed (bonded) on the second surface 323 of the light guideplate 321, and diffracts and reflects the parallel light, whichpropagates in the light guide plate 321 by total reflection, multipletimes, and emits the parallel light from the light guide plate 321through the first surface 322.

The parallel light also propagates in the light guide plate 321 by totalreflection, and is then emitted. In this case, since the light guideplate 321 is thin and the optical path in the light guide plate 321 islong, the number of total reflections made until the light beams reachthe second diffraction grating member 340 varies according to the angleof view. More specifically, the number of reflections of parallel lightthat is incident at an angle such as to approach the second diffractiongrating member 340, of parallel light incident on the light guide plate321, is smaller than the number of reflections of parallel light that isincident on the light guide plate 321 at an angle such as to get awayfrom the second diffraction grating member 340. This is because theparallel light, which is diffracted and reflected by the firstdiffraction grating member 330 and is incident on the light guide plate321 at the angle such as to approach the second diffraction gratingmember 340, forms a smaller angle to the normal angle at the light guideplate 321 when the light propagating in the light guide plate 321impinges on the inner surface of the light guide plate 321, than theparallel light that is incident on the light guide plate 321 at theangle in the opposite direction. The shape of the interference fringesformed in the second diffraction grating member 340 and the shape of theinterference fringes formed in the first diffraction grating member 330are symmetrical with respect to an imaginary plane perpendicular to theaxis of the light guide plate 321.

The light guide plate 321 in Example 4 that will be described below hasthe same configuration and structure as those of the light guide plate321 described above.

Since the head mounted display of Example 3 has substantially the sameconfiguration and structure as those of the head mounted display ofExample 1 except that the optical device 320 is different, as describedabove, a detailed description thereof is omitted.

Example 4

Example 4 is a modification of Example 3. FIG. 7 is a conceptual view ofan image display apparatus in a head mounted display according toExample 4. In an image display apparatus 400 of Example 4, a lightsource 251, a collimating optical system 252, a scanning member 253, aparallel light emitting optical system (a relay optical system 254),etc. have the same configuration and structure (the image forming devicehaving a second configuration) as those adopted in Example 2. Further,an optical device 320 has the same configuration and structure as thoseof the optical device 320 in Example 3. Since the head mounted displayof Example 4 has substantially the same configuration and structure asthose of the head mounted display of Example 1 except theabove-described differences, a detailed description thereof is omitted.

Example 5

Example 5 is a modification of Example 1. The propagation of light in alight guide plate that forms the image display apparatus of Example 5 isschematically shown in FIG. 8A, and a conceptual diagram showing anarrangement state of a light guide plate, etc. that forms the imagedisplay apparatus of Example 5 is shown in FIG. 8B. Here, in Example 5,the optical axis of the optical system (the parallel light emittingoptical system or the collimating optical system) 112 is parallel to theYZ plane, is parallel to the XY plane, and passes through a positionshifted from the center of the image forming device 111. By adoptingsuch a configuration, the central light beam CL is included in the YZplane, and intersects the XY plane at an elevation angle θ.

Example 6

Example 6 is a modification of Examples 1 to 5, and relates to a headmounted display according to a second embodiment of the invention. Aview when a state where the image display apparatus of Example 6 is wornon the head of an observer is obliquely viewed is shown in FIG. 9, aview when the image display apparatus is viewed from the front is shownin FIG. 10, a view when the image display apparatus is viewed from theside is shown in FIG. 11, and a view when the image display apparatus isviewed from above is shown in FIG. 12. Although these drawings show thatthe image display apparatus is worn on the head of an observer, theyshows a state before the image display apparatus pivots downward withrespect to the frame, with a virtual straight line connecting thecenters of two eyeballs of the observer who observes the image displayapparatus as a pivot axis.

Similarly to those described in Examples 1 to 5, the head mounteddisplay of Example 6 includes (a) a frame shaped like glasses 50 to beworn on the head of an observer, and

(b) an image display apparatus 100, 200, 300, or 400 attached to theframe 50, and the image display apparatus 100, 200, 300, or 400includes:

(A) an image forming device 111 or 211;

(B) an optical system (a parallel light emitting optical system) 112 or254 which converts the light emitted from the image forming device 111or 211 into parallel light, and

(C) an optical device 120 or 320 which the light beams converted intothe parallel light by the optical system 112 or 254 enter, and areguided therein, and emitted therefrom.

The image display apparatus 100, 200, 300, or 400 is pivotally attachedto the frame 50, with a virtual straight line connecting the centers oftwo eyeballs of the observer who observes the image display apparatus100, 200, 300, or 400 as a pivot axis RX. Specifically, in the headmounted display of Example 6, at least one of the image forming device111 or 211, the optical system 112 or 254, and the optical device 120 or320 (more specifically, the image forming device 111 or 211, the opticalsystem 112 or 254, and the optical device 120 or 320 are integrated, andgenerally all of these) is pivotally attached to the frame 50. In thehead mounted display of Example 6, when an observer views a horizontallylocated object, a central light beam that is emitted from the opticaldevice and enters the eyes of the observer forms a depression angle, andthe depression angle with respect to the horizontal plane is, forexample, 5 degrees to 45 degrees.

In the head mounted display of Example 6, the frame 50 is formed by afront portion 51 arranged at the front of an observer, and two templeportions 53 attached to both ends of the front portion 51 in a fixedstate. A tip portion of each temple portion 53 is formed by a U-shapedmember. In the following description, a tip portion of the templeportion 53 equivalent to a U-shaped upper crossbar is referred to as a“first member 53A”, a tip portion of the temple portion 53 equivalent toa U-shaped lower crossbar is referred to as a “second member 53B”, and atip portion of the temple portion 53 equivalent to a U-shapedlongitudinal bar is referred to as a “third member 53C”. The secondmember 53B is attached to both ends of the front portion 51 in a fixedstate. An arm portion (handle portion) 53D further extends toward an endcover portion 54 from the third member 53C. Two end cover portions 54are connected together by a holding band 55 to prevent the head mounteddisplay from shifting when the head mounted display is worn on a head.Such a mounting band can be incorporated even in Examples 1 to 5.

The image forming device 111 or 211 is stored in the space that issandwiched between the first member 53A and the second member 53B, andis surrounded by the first member 53A, the second member 53B, and thirdmember 53C. Specifically, a recessed portion (not shown) is provided inthe image forming device 111 or 211 that faces the first member 53A, andthe face of the first member 53A that faces the image forming device 111or 211 is provided with a projection portion (not shown) that fits therecessed portion. Further, the image forming device 111 or 211 thatfaces the second member 53B is provided with a threaded hole portion(not shown), and the second member 53B that faces the image formingdevice 111 or 211 is provided with a through hole. Then, the imageforming device 111 or 211 can be attached to the tip portion of thetemple portion 53 by fitting the recessed portion provided in the imageforming device 111 or 211 to the projection portion provided in thefirst member 53A, passing a screw (the head of a screw 56 is shown inFIG. 11 only) through the through hole provided in the second member53B, and screwing the screw 56 into the hole portion provided in theimage forming device 111 or 211. From the viewpoint of reliablyattaching the image forming device 111 or 211 to the tip portion of thetemple portion 53, it is preferable that a push spring be inserted intoa shank of the screw 56 between the head of the screw 56 and the imageforming device 111 or 211. A straight line connecting the projectionportion provided in the first member 53A and the screw 56, and a virtualstraight line connecting the centers of two eyeballs of an observer arelocated on the pivot axis RX. The image display apparatus 100, 200, 300,or 400 can be pivotally attached to the frame 50, with the virtualstraight line connecting the centers of two eyeballs of the observer asthe pivot axis RX. In addition, the attaching mechanism and attachingmethod of the image display apparatus 100, 200, 300, and 400 describedabove are merely illustrative, and can be suitably altered. Even if astraight line connecting the projection portion provided in the firstmember 53A and the screw 56, and the virtual straight line connectingthe centers of two eyeballs of an observer are slightly shifted fromeach other, i.e., when the distance between the virtual straight lineconnecting the centers of two eyeballs of the observer, and the pivotaxis RX is a maximum of 6.5 mm, there is no case where an image emittedfrom the image display apparatus 100, 200, 300, or 400 is substantiallymoved away from the eyes of the observer. Thus, it is assumed that theimage display apparatus 100, 200, 300, or 400 is pivotally attached tothe frame 50, with a virtual straight line connecting the centers of twoeyeballs of an observer who observes an image display apparatus as apivot axis.

Since the image display apparatus and the light guide plate in Example 6can have the same configuration and structure as the image displayapparatus and the light guide plate which are described in Examples 1 to5, a detailed description thereof is omitted.

Since the image display apparatus 100, 200, 300, or 400 that forms thehead mounted display of Example 6 is pivotally attached to the frame 50,with a virtual straight line connecting the centers of two eyeballs ofthe observer who observes the image display apparatus as a pivot axisRX, even when the image display apparatus 100, 200, 300, or 400 is movedin a vertical direction by pivoting the image display apparatus 100,200, 300, or 400, there is no case where an image emitted from the imagedisplay apparatus 100, 200, 300, or 400 is moved away from the eyes ofan observer.

In addition, even when it is unnecessary to display a display imagewhile being shifted to a position above or below a horizontal line ofsight of an observer, when it is necessary to pivot the image displayapparatus to move the image display apparatus in the vertical direction,thereby optimizing the position of the image display apparatus, themechanism, configuration, and structure which allows the central lightbeam to intersect the XY plane at angles (θ) other than 0 degree asdescribed in Examples 1 to 5 are unnecessary. The image displayapparatus has only to be pivotally attached to the frame, with a virtualstraight line connecting the centers of two eyeballs of an observer whoobserves the image display apparatus as a pivot axis.

Although the invention has been described above on the basis of thepreferable embodiments, the invention is not limited to theseembodiments. The configuration and structure of the image displayapparatus and the head mounted display that have been described in theembodiments are merely illustrative, and can be suitably altered. Forexample, a surface relief-type hologram (refer to US Patent ApplicationPublication 2004/0062505A1) may be arranged in the light guide plate.The optical device 320 of Example 3 or 4, can also be embodied so thatthe diffraction grating element is formed by a transmissive diffractiongrating element, or any one of the first deflecting member and thesecond deflecting member is formed by a reflective diffraction gratingelement, and the other is formed by a transmissive diffraction gratingelement. Alternatively, a reflective blazed diffraction grating elementcan also be used as the diffraction grating element.

The present application contains subject matter related to thosedisclosed in Japanese Priority Patent Applications JP 2009-199567 and JP2009-280133 filed in the Japan Patent Office on Aug. 31, 2009 and Dec.10, 2009, respectively, the entire contents of which is herebyincorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A head mounted display comprising: (a) a frameshaped like glasses to be worn on the head of an observer; and (b) animage display apparatus attached to the frame, the image displayapparatus including (A) an image forming device; (B) an optical systemthat converts light emitted from the image forming device into parallellight; and (C) an optical device to which the light beams converted intothe parallel light by the optical system enter, in which the light beamsare guided, and from which the light beams are emitted, wherein when apoint where a central light beam that is emitted from the center of theimage forming device and passes through the nodal point of the opticalsystem on the side of the image forming device enters the optical deviceis defined as an optical device center point, an axis that passesthrough the optical device center point, and is parallel to the axisdirection of the optical device is defined as an X-axis, and an axisthat passes through the optical device center point, and coincides withthe normal axis of the optical device is defined as a Y-axis, thecentral light beam intersects the XY plane at angles other than 0degree.
 2. The head mounted display according to claim 1, wherein theimage display apparatus is pivotally attached to the frame, with avirtual straight line connecting the centers of two eyeballs of theobserver who observes the image display apparatus as a pivot axis. 3.The head mounted-display according to claim 2, wherein at least one ofthe image forming device, the optical system, and the optical device ispivotally attached to the frame.
 4. The head mounted display accordingto claim 1, wherein the central light beam is included in the YZ plane.5. The head mounted display according to claim 1 or 4, wherein theoptical axis of the optical system is included in the YZ plane andintersects the XY plane at angles other than 0 degree.
 6. The headmounted display according to claim 1 or 4, wherein the optical axis ofthe optical system is parallel to the YZ plane, is parallel to the XYplane, and passes through a position shifted from the center of theimage forming device.
 7. The head mounted display according to claim 1,wherein assuming that the XY plane coincides with the horizontal plane,the angle θ at which the central light beam intersects the XY plane isan elevation angle.
 8. The head mounted display according to claim 7,wherein the XY plane intersects the vertical plane at angles other than0 degree.
 9. The head mounted display according to claim 8, wherein theXY plane intersects the vertical plane at an angle θ.
 10. The headmounted display according to any one claims 7 to 9, wherein the maximumvalue of θ is 5 degrees.
 11. The head mounted display according to claim1, wherein when an observer views a horizontally located object, acentral light beam that is emitted from the optical device and entersthe eyes of the observer forms a depression angle.
 12. The head mounteddisplay according to claim 1, wherein the frame is formed by a frontportion arranged at the front of an observer, and two temple portionspivotally attached to both ends of the front portion via hinges.
 13. Ahead mounted display comprising: (a) a frame shaped like glasses to beworn on the head of an observer; and an image display apparatus attachedto the frame, the image display apparatus including (A) an image formingdevice; (B) an optical system that converts light emitted from the imageforming device into parallel light; and (C) an optical device to whichthe light beams converted into the parallel light by the optical systementer, in which the light beams are guided, and from which the lightbeams are emitted, wherein the image display apparatus is pivotallyattached to the frame, with a virtual straight line connecting thecenters of two eyeballs of the observer who observes the image displayapparatus as a pivot axis.
 14. The head mounted display according toclaim 13, wherein at least one of the image forming device, the opticalsystem, and the optical device is pivotally attached to the frame. 15.The head mounted display according to claim 13, wherein when an observerviews a horizontally located object, a central light beam that isemitted from the optical device and enters the eyes of the observerforms a depression angle.
 16. An image display apparatus comprising: (A)an image forming device; (B) an optical system that converts lightemitted from the image forming device into parallel light; and (C) anoptical device to which the light beams converted into the parallellight by the optical system enter, in which the light beams are guided,and from which the light beams are emitted, wherein when a point where acentral light beam that is emitted from the center of the image formingdevice and passes through the nodal point of the optical system on theside of the image forming device enters the optical device is defined asan optical device center point, an axis that passes through the opticaldevice center point, and is parallel to the axis direction of theoptical device is defined as an X-axis, and an axis that passes throughthe optical device center point, and coincides with the normal axis ofthe optical device is defined as a Y-axis, the central light beamintersects the XY plane at angles other than 0 degree.
 17. The imagedisplay apparatus according to claim 16, wherein the central light beamis included in the YZ plane.
 18. The image display apparatus accordingto claim 16 or 2, wherein the optical axis of the optical system isincluded in the YZ plane and intersects the XY plane at angles otherthan 0 degree.
 19. The image display apparatus according to claim 16 or2, wherein the optical axis of the optical system is parallel to the YZplane, is parallel to the XY plane, and passes through a positionshifted from the center of the image forming device.
 20. The imagedisplay apparatus according to claim 16, wherein the optical deviceincludes: (a) a light guide plate from which incident light is emittedafter the light propagates in the light guide plate by total reflection;(b) a first deflecting means for deflecting the light incident on thelight guide plate so that the light incident on the light guide plate istotally reflected in the light guide plate; and (c) a second deflectingmeans for deflecting the light, which propagates in the light guideplate by total reflection, multiple times so as to emit the light, whichpropagates in the light guide plate by total reflection, from the lightguide plate, and wherein the central point of the first deflecting meansis the optical device center point.